Well-known radio frequency heating apparatus include an electric generator which produces a voltage oscillating at a predetermined frequency, typically established by international rules and equivalent to 6.78-13.56-27.12 or 40.68 MHz, and a capacitive or inductive application device transforming the oscillating voltage in an oscillating electric or magnetic field, respectively.
If the food products have a substantially dielectric behaviour, capacitive application devices are normally used which generate an oscillating electric field involving the food product. The dielectric loss within the product causes the heating thereof. On the contrary, if the food products substantially have a conductive behaviour, inductive application devices are normally used which generate an oscillating magnetic field involving the food product. The electric currents so induced to the conductive product cause the heating thereof.
Tests have been made on meat-products, such as hams, mainly made of meat, fats and salts. This combination of substances behaves in a way which is neither fully dielectric nor fully inductive. Particularly, it has been noted that if an electric field oscillating at 27.12 MHz is applied to a ham having a considerable mass, the electric field hardly penetrates the food product, thus heating quickly enough a layer which is about 2-3 cm thick, while the internal part of the products can not be heated satisfactorily. For this reason, the well-known apparatus operating according to the principle of the dielectric loss can effectively cook meat-products only when the mass and volume of said products are relatively small.
Another problem affecting the above-mentioned known apparatus is that the distance between the frame of the capacitive application device and the meat-products must be as little as possible. For this reason such apparatus are almost exclusively used to cook products having predetermined geometric shapes, usually a tubular shape.
Cooking tests have been made on meat-products having a considerable mass also by using apparatus having inductive application devices. In this case, it has been found that the products can be heated more quickly than by using the dielectric loss system but, however, it does not ensure a total penetration of the field into the mass of the meat-product because of the imperfect, incomplete and non-homogeneous conductive behaviour of the product.
This invention has the purpose to solve the problems encountered when cooking and/or heating by radio frequency meat-products by means of the well-known apparatus.
Another purpose of this invention is to provide an apparatus which may be easily and economically manufactured, used and maintained, and which may be used also in the case that foodstuffs must be placed into moulds having various shapes.